ISO week number to date
When a shipment or delivery is quoted as a week number such as W14, this shows the actual dates of that week.
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How to use it
- Enter year and week number.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Monday of week 1 = 4 January − (its ISO weekday − 1), Monday = 1. Monday of week n = Monday of week 1 + (n − 1) × 7, and Sunday = Monday + 6.
Example
Inputs: Year = 2,026, Week number = 40. Result: Week starts (Monday): Monday, September 28, 2026 (2026-09-28); Week ends (Sunday): Sunday, October 4, 2026 (2026-10-04); Weeks in that year: 53.
Limits and caveats
- Follows ISO 8601 only, where weeks start on Monday even if your work week starts on Sunday.
Questions about this tool
Why does week 1 sometimes start in December?
Week 1 is the week containing 4 January, so its Monday can fall in late December.
Why is week 53 rejected?
Most years have 52 weeks; week 53 exists only in long years such as 2020 and 2026.
What does 2026-W40 mean?
It is the standard way to write week 40 of ISO week-year 2026.